This is what 120 calories of low fat ice cream looks like. If you were to go by the container, and use volume say "a half cup" you could easily put in twice as much. Or you want to use a "tablespoon" of olive oil, and pull out your actual tablespoon and use that, you might be overshooting the actual serving size weight by about 40%. Every little bit counts when you're trying to make weight loss progress
Same goes for dry ingredients like cereal, other stuff. It's amazing how much packaging lies to you. Let's say you eat an entire bag of doritos and you think it's 2000 calories for example; if you actually weighed it you'd find it out it might've been 2300 because most of the time they give you more